The present invention relates to synthesis of thermolabile multifunctional azo compounds and their use for the preparation of high molecular weight well-defined structured polymers. As described for example in U.S. Pat. Nos. 6,605,674, 6,627,719, and 6,753,388 these azo compounds are particularly useful for the synthesis of flocculants, coagulants and dispersants for paper, mining and wastewater industries.
Well-defined macromolecular architectures are typically prepared by living anionic or cationic polymerization or by controlled radical polymerizations such as RAFT (Reversible addition-fragmentation chain transfer), ATRP (Atom Transfer Radical Polymerization), NMP (Nitroxide-Mediated Polymerization) and more recently SET-LRP (Single Electron Transfer-Living Radical Polymerization). Each of these methods have limitations, such as monomer compatibility, purity of reactants, reaction medium, heavy metal contamination in the final product, longer reaction times, and an inability to achieve high molecular weights. From an industrial point of view these polymerizations are not enticing due to the processing cost and selectivity towards monomers and reaction conditions. Traditional free radical polymerization is widely used industrially for polymer synthesis, due to the ease of synthesis and the ability to avoid the limitations of the prior methods. However, the ability to control the concise architecture of the final product using traditional free radical methods is limited.
There are many ways to manipulate the architecture of macromolecules. Star polymers gained much attention in the last two decades and there have been numerous publications on its synthesis and properties of the resulting polymers. The two most common ways to make star polymers are (1) start with a multifunctional initiator (as shown in FIG. 1) and (2) covalently attach a preformed polymer to a polyfunctional core. Polyfunctional initiators result in polymers of high molecular weights and in the synthesis of very large macromolecules (MW several millions) the first route is the preferred method of preparation.
Synthesis of linear macromolecules from azo initiators are widely known and have been practiced for many years. AIBN (Azobisisobutyronitrile) is one of the most commonly used initiator molecule in the industry and academia due to its cost, availability, solubility and decomposition temperature. Upon decomposition a molecule such as AIBN generates a molecule of N2 and two equally reactive radicals capable of initiating polymerization, which could lead to two linear polymers. There are numerous publications available on the manipulation of azo groups to gain better control on the final architecture of the macromolecule. Several detailed reviews on azoderivatives are available in the literature; especially reviews by C. I. Simionescu et al. covers most of the work done in this area. (Prog. Polym. Sci., 1986, 12, 1-109; Romanian chemical quarterly reviews 1995; 3(2), 83-103).
There are very few useful multifunctional initiators capable of initiating polymerization. The main drawback with multifunctional initiators is that upon decomposition, a second radical produces linear polymers in addition to the desired star polymers. For example, (as illustrated in FIG. 3) a prior art composition commercially known as Arkema's Luperox JWEB50 is a multifunctional (four functional) organic peroxide, which upon decomposition yields a tetra functional initiator and four tertbutoxy radicals which each could produce linear polymers. (Penlidis et al,: Poly Bull 2006, 57, 157-167 and Penlidis et al.: Macromol Chem Phys 2003, 204, 436-442). In order to exclusively make structured polymer these tertbutoxy radicals need to be prevented from initiating polymerization reactions.
U.S. Pat. No. 4,929,721 teaches the preparation of azo side groups on the polymer backbone by copolymerization. The azo groups on the resulting polymer may be used for post modification of the polymer. The azo groups reported by this patent have two main problems; first, the decomposition temperature of this molecule is too high to be practically used as a polymerization initiator for inverse emulsion polymerization. Their objective was to keep this molecule stable during polymerization and activate only for post modification. This patent reports their compounds to be very stable at 130° C. The second problem with this approach is that this will also create the linear polymers in addition to graft co-polymers.
International Patent Application WO/0224773 teaches the synthesis of branched polymers. In this teaching they have taken into account of the fact there could be linear polymers formed. This was eliminated by making sure the second radical is unable to initiate the polymerization. However, this teaching also fails to make well-defined cores to make well-defined star polymers. Both of the above teachings makes use of the vinyl groups to homo or co-polymerize the azo groups onto a polymer and the azo groups are activated at a later time for further modification of the polymer or at the same time to make highly random branches. Activation of the azo side groups at the same time as the backbone synthesis will lead to highly branched but a poorly defined architecture. This approach in flocculant synthesis will result in highly closed architecture, which are known to be very ineffective.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.